fix(billing): reject saturated pre-consume quota

pkg/billingexpr/round.go

@@ -12,3 +12,10 @@ import "github.com/QuantumNous/new-api/common"
 func QuotaRound(f float64) int {
 	return common.QuotaRound(f)
 }
+
+// QuotaRoundChecked is QuotaRound but also reports whether the result had to
+// be saturated. Pre-consume callers use this to reject an unrepresentable
+// estimate before any quota is deducted.
+func QuotaRoundChecked(f float64) (int, *common.QuotaClamp) {
+	return common.QuotaRoundChecked(f)
+}